674 MUSCLES OF THE PELVIS. 



it and the insertion of the glutens medius. Function. The 

 same as the last, and also to strengthen the ilio-femoral 

 articulation. 



The pyriformis (Fig. 212) is a triangular muscle, which 

 arises by its base within the pelvis, fleshy and tendinous, 

 from the second, third, and fourth divisions of the sacrum, 

 and forms a thick, conical belly, which passes out at the upper 

 part of the great sciatic notch, receiving fibres in its course, 

 from the sciatic ligament and posterior inferior part of 

 the ilium. It is inserted by a round tendon into the su- 

 perior portion of the fossa at the root of the trochanter 

 major. Function. To rotate the thigh outward. 



The gemelli (Fig. 212) are two small muscles. The supe- 

 rior arises from the spine of the ischium, the inferior from 

 the tuber of the ischium and the great sciatic ligament- 

 They run parallel to each other, and both are inserted into 

 the root of the trochanter major. 



Function. To rotate the thigh outward, and strengthen 

 the capsular ligament. 



The obturator internus (Fig. 212) arises from the pelvic 

 surface of the obturator ligament, except at the superior 

 part where the obturator vessels and nerve pass out ; also 

 from the obturator margin and plane of the ischium. Its 

 fibres converge to a flat tendon, which passes through the 

 lesser sciatic foramen, and thence goes between the gemelli 

 muscles to be inserted into the fossa at the root of the 

 great trochanter. As this muscle passes over the ischium, 

 there is found interposed a bursa, and another between the 

 tendon and the gemelli. 



Function. To rotate the thigh outward. 



Obturator Externus. Dissection. Most of the muscles on 

 the anterior and internal thigh at the superior part must 

 be removed, when this muscle will be seen to arise fleshy 

 from the anterior surface of the obturator ligament, except 

 where the obturator vessels pass out, and also from the 

 surrounding margin of the thyroid foramen. The fibres 

 converging, end in a tendon which passes outward and 

 ackward in a groove behind the neck of the femur, to be 



